It seems there is suddenly something out of sync with asp.net core packages.
It looks like Microsoft.AspNetCore.App 2.1.1 was released 16 hours ago on nuget.org but
I had the same issue. Another option is, in NuGet Package Manager, rollback Microsoft.AspNetCore.All, Microsoft.AspNetCore.Rewrite, and Microsoft.NETCore.App to versions 2.1.0.